The present invention relates to microwave oscillators. In particular, the present invention is a nanoscale oscillator device which generates microwave output by applying a DC electric current through a layered magnetic structure with nanometer dimensions.
“Spin Momentum Transfer” (SMT) or “Spin Torque Transfer” was predicted to exist by Slonczewski in an article published in Phys. Rev. B, Volume 39(10), 6995, 1989. Since that time, Spin Momentum Transfer has been an area of interest primarily for use in MRAM devices. In 2005, two groups (one based at the National Institute of Standards and Technology (NIST) in Boulder, Colo., and the other at Free Scale Semiconductor Inc. in Chandler, Ariz.) reported experimental results of phase-locked microwave spin transfer or spin torque oscillators: Kaka et al., “Mutual Phase-locking of Microwave Spin Torque Nano-oscillators”, Nature, Vol. 437 (15), 389-392 (September 2005). Mancoff et al., “Phase-locking in Double-Point-Contact Spin-Transfer Devices” Nature, Vol. 437 (15), 393-395 (September 2005).
In addition to these two articles, there have been other publications which have also discussed spin momentum transfer as a mechanism for an oscillator in the GHz spectrum. These include: Pufall, “Large-angle, Gigahertz-Rate Random Telegraph Switching Induced by Spin-Momentum Transfer”, Phys. Rev. B, 69, 214409 (2004); Wolf et al., “Spintronics—A Retrospective and Perspective,” IBM J. Res. & Dev. Vol. 50, No. 1, 101-109 (January 2006); Kazakova et al., “NPL Report” DEM-TQD-002 “Metrological Challenges of Nanomagnetism,” section 4.2.2.3, pages 27-28 (October 2005); Ralph et al., “Coherence of Microwave-Frequency Nanomagnetic Dynamics Driven by a DC Spin-Polarized Current,” Cornell NanoScale Facility Project #598-96, page 260; Rippard et al., “Injection Locking and Phase Control of Spin Transfer Nano-oscillators,” Physical Review Letters, PRL 95, 067203 (2005); and Sun, “Spin Angular Momentum Transfer in Current-Perpendicular Nanomagnetic Junctions,” IBM J. Res. & Dev., Vol. 50, No. 1 (2006).